This invention relates to ultrasonic diagnostic imaging systems and, in particular, to ultrasonic diagnostic imaging systems which automatically define the borders and boundaries of structures within an ultrasonic image.
Many ultrasonic diagnostic procedures in which bodily functions and structures are quantified rely upon clear delineation and definition of the body structures and organs which are being measured. When the quantification or measurement procedure uses static images or a small set of measurements, the delineation of the bodily structure being measured can be done manually. An example of such a procedure is the obstetrical measurements of a developing fetus. Static images of the developing fetus can be acquired during periods when fetal activity is low. Once an image is acquired, only a few circumference or length measurements are usually required to compute development characteristics such as gestational age and anticipated delivery date. These measurements can readily be made manually on the fetal images. Other diagnostic procedures, particularly those involving measurements of the heart and its functioning, present a further set of difficulties. The heart is always beating and hence is always in motion. As it moves, the contours of the heart constantly move and change as the organ contracts and expands. To fully assess many characteristics of cardiac function it is necessary to evaluate many and at times all of the images acquired during the heart cycle (one heartbeat), which can amount to thirty to one hundred and fifty or more images. The structure of interest such as the endocardium, epicardium or valves must then be delineated in each of these images, a painstaking, time-consuming task. Since these structures are constantly in motion, they appear slightly different in each image acquired during the cardiac cycle, and can also vary significantly from one patient to another. While applications such as obstetrical procedures would benefit from a processor which automatically delineates specific anatomy in an ultrasonic image, cardiac diagnosis would benefit even more so. Quantification of cardiac function often relies on the delineation of structure as an input. For example, although myocardial wall thickening is currently assessed in stress-echocardiographic exams, the degree of wall thickening is typically qualitatively scored by the clinician without the use of measurement tools because segmental measurements over the cardiac cycle are too time-consuming. Techniques for assessing blood perfusion information provided by contrast agents or Doppler techniques also benefit from delineation of the cardiac borders since they often require that the myocardial area be delineated before the assessment can proceed.
Research into systems that automatically analyze ultrasound images and draw borders around objects in the images has been underway for over a decade, challenged by the specular nature and speckle noise of ultrasound images and the variability with which tissue structures may appear in an image. While the ultimate goal is a system which will delineate borders and boundaries automatically without any user input, many of the systems proposed to date have taken assisted or semi-automatic approaches. In these approaches the user manually marks key reference points in an image, or draws the complete border of an object in one image. A semi-automatic system uses these manual inputs as references from which the balance of a border or other borders will be drawn. This need for user input limits semi-automatic techniques to operating only with stored images and prevents their use in real time. Thus, a need remains for an automated border detection system that can reliably delineate the border of an object in an ultrasound image without user preconditioning, and does so in real time.
In accordance with the principles of the present invention, a technique for automatically delineating the border or boundary of an object in an ultrasound image is described. The inventive technique locates key landmarks of the object in the image, then fits one of a plurality of predefined standard shapes to the key landmarks and the object. In a cardiac embodiment the ultrasound system displays both the end systole and end diastole images of a cardiac cycle and the borders drawn on both images. The user may automatically adjust the automatically drawn borders by a rubber-banding technique. The user has a choice of selecting a cardiac cycle upon which borders will be automatically drawn, or to view a sequence of images with automatically drawn borders from which a cardiac cycle is selected. The inventive technique may be advantageously used to compute ejection fraction or to analyze local heart wall motion over the full cardiac cycle.